The present invention relates to a wear-resistant compound roll, and more particularly to a wear-resistant compound roll having high strength, wear resistance and resistance to surface roughening.
With respect to rolls, increasingly higher wear resistance and resistance to surface roughening have been required to prevent the deformation of rolled products due to the wear of the rolls and to reduce the frequency of exchanging rolls. In conventional centrifugal cast rolls, to prevent the gravitational segregation in shell portions and to achieve the graphitization of cast alloys for the shaft portions for the purpose of having higher toughness, the shell portions should have particularly limited chemical compositions. As a result, the above demands are not satisfied in the centrifugal cast rolls.
In such circumstances, the inventors previously proposed, as a method of producing a new roll free from the above restriction of the chemical composition of a shell portion, a continuous casting method for forming a shell portion around a shaft portion by using a high-frequency coil (Japanese Patent Laid-Open No. 61-60256, WO 88/07594 corresponding to U.S. Pat. No. 4,958,422 issued Sept. 25, 1990). By the development of such a method, elements such as V, W, Mo, etc. capable of forming hard carbides can be added to a shell portion material in large amounts, thereby providing rolls having durability several times higher than the conventional centrifugal cast rolls. However, it has been found that such rolls are not necessarily satisfactory in a resistance to surface roughening. This means that depending upon the conditions of using rolls, the surface roughening may take place, resulting in a rolling durability only about two times that of the conventional centrifugal cast rolls.
As a result of investigation on the surface roughening and the alloy structure of the roll, the inventors have found that the surface roughening phenomenon of the wear-resistant compound roll has a close relation with the microstructure of the shell portion, and that by controlling the microstructure, the resistance to surface roughening can be greatly improved. On the other hand, when there are a lot of non-granular carbides, particularly network-shaped carbides in the microstructure, cracks are generated predominantly at the sites of these carbides and propagate therefrom, thereby causing surface roughening due to such cracks.